Cryogenic cooling systems are employed in various demanding applications including military and civilian active and remote sensing, superconducting, and general electronics cooling. Such applications often demand efficient, reliable, and cost effective cooling systems that can achieve extremely cold temperatures, e.g., below 140 Kelvin and minimize the consumption of valuable and scarce size and weight capacities.
In an effort to address the forgoing applications, Joule-Thomson (J-T) microcoolers have been employed. As used herein and throughout this specification, the term “microcooler” shall be understood to include: cryocoolers, cryostats, and the like with microscale features (features with sizes on the order of 1 to 1000 microns, where 1 micron is one micrometer, μm, 1 μm=10−6 meters). Briefly, J-T cooling occurs when a non-ideal gas compressed at high pressure encounters low pressure and expands adiabatically (i.e., at constant enthalpy). This is typically achieved on the microscale by connecting a high pressure microchannel through a smaller width orifice (often part of a tapered nozzle) to a relatively wide microchannel, such as a microscale expansion chamber.
Undesirably, conventional J-T microcoolers oftentimes suffer from failure caused by clogging within small orifices, nozzles and/or channels through which the cooling fluid passes. The clogging may occur as a result of impurities or particulates forming at the inlet/outlet ports of the microcooler. These impurities and/or particulates can originate as condensable organic gasses, water, dust, compressor oils, manufacturing residues and/or combinations thereof formed by the refrigeration process.
In macro-scale J-T cryocoolers, the clogging problem is generally solved mechanically by destabilizing the orifice mechanism in response to gas flow or temperature conditions in the input line or gas reservoir. For example, a system may have a plunger duct which expands to allow particulate matter through when changes in the incoming gas flow rate is sensed. Unfortunately, implementation of mechanically reactive orifices is not practical or economical in J-T microcoolers due to materials, processing and the dominance of adhesive forces over inertial forces associated with such small physical scales.